The marketing of certain types of produce, for example bananas, required that the produce be acquired in an unripe state and brought to a desired state of ripeness in varying but accurately predictable periods of time chosen in anticipation of market requirements.
The ripening rate of produce is predominately a function of the temperature of the produce and the ripening process is carried out by placing the produce in enclosures in which the temperature is controlled to give the desired rate. The ripening rate of produce such as bananas changes greatly for a temperature change as little as one degree and, if the produce temperature goes outside rather narrow limits, the produce may be ruined. Inaccurate temperature control, or a failure of the temperature control means, can thereby lead to substantial economic loss.
Previous temperature control devices have had the drawback of insufficient accuracy of temperature control and of insufficient accuracy in selection of the temperature, requiring a trial and error process dependent upon the skill of the operator.
The temperature control device must also provide a warning when the actual temperature of the produce goes outside of allowable limits. It is necessary for the warning to operate when there is a failure of power to the device.
As there are usually a minimum of personnel to monitor the ripening processes, it is necessary to give effective warning of a temperature error or power failure. It is also necessary to be able to add or disconnect enclosures from the warning without major modifications.
It is necessary to place the temperature control device in contact with the produce to accurately monitor the produce temperature. This requires that personnel handling the produce be protected from dangerous voltages existing in the heating, cooling and fan equipments connected to the temperature control device.